Mechanisms underlying the maintenance of muscle hypercontractility in a model of postinfective gut dysfunction

Interaction between interleukin-17-producing CD4+ T cells and colonic subepithelial myofibroblasts: what are they doing in mucosal inflammation?

Recent studies have shown alterations and activations in the mucosal immune system in patients with irritable bowel syndrome (IBS) as well as in those with inflammatory bowel disease (IBD). As one of effectors of mucosal inflammation, a new lineage of effector CD4+ T cells characterized by production of interleukin (IL)-17, the T-helper (Th)-17 lineage, was recently described. Th-17 cells are developmentally and functionally distinct from Th1 and Th2 cells. Here, we discuss the recent concept of low-grade inflammation as a factor associated with the pathophysiology of IBS. Furthermore, based on the data from our laboratory, interaction between Th-17 cells and colonic subepithelial myofibroblasts may play an important role in the pathophysiology of IBS and IBD.

Neural mechanisms of early postinflammatory dysmotility in rat small intestine

Although human postinflammatory dysmotility is known, so far animal studies have primarily investigated changes during inflammation. Here, we focused on postinflammatory changes in rat jejunal myenteric plexus and jejunal motility. Evolution of ethanol/2,4,6-tri-nitrobenzene sulphonic acid (TNBS)-induced inflammation was assessed histologically and by measuring myeloperoxidase activity (MPO). Electromyography and immunohistochemistry were performed 1 week after ethanol/TNBS and also after N(G)-nitro-L-arginine methyl ester (L-NAME) administration. Ethanol/TNBS induced a transient inflammation, with normalization of MPO and histological signs of an early phase of recovery after 1 week. The number of cholinergic neurones was not altered, but myenteric neuronal nitric oxide synthase (nNOS)-immunoreactivity was significantly lower in the early phase of recovery after TNBS compared with water (1.8 +/- 0.2 vs 3.5 +/- 0.2 neurones ganglion(-1), P < 0.001). Interdigestive motility was disrupted with a loss of phase 1 quiescence, an increase of migrating myoelectric complex cycle length, a higher number of non-propagated activity fronts and a decrease of adequately propagated phase 3 s after TNBS. Administration of L-NAME resulted in a similar disruption of interdigestive motility patterns. In the early phase of recovery after ethanol/TNBS-induced jejunal inflammation, a loss of motor inhibition occurs due to a decrease of myenteric nNOS activity. These observations may provide a model for early postinflammatory dysmotility syndromes.

Contribution of gender to pathophysiology and clinical presentation of IBS: should management be different in women?

The irritable bowel syndrome (IBS) is found more commonly in women than men. It is more prevalent in patients with chronic fatigue syndrome, fibromyalgia, and chronic pelvic pain, all syndromes characterized by pain and found predominantly in women. This article reviews evidence for a role of biological sex factors and gender on the pathways mediating visceral pain. The effect of gonadal hormones on gastrointestinal motility and the sensory afferent pathway and central processing of visceral stimuli and the contribution of gender role to the clinical presentation are discussed. Although differences in responses to treatment modalities between genders exist, the approach to IBS patients in both genders is quite similar. Nevertheless, a special attention to gender role and stress-related factors should be addressed. New developments in research, outlined in the paper, might bring more gender-specific treatments in the future.

Allergy and intestinal dysmotility--evidence of genuine causal linkage?

PURPOSE OF REVIEW

The relationship between allergy and motility has been controversial. There is, however, accumulating evidence demonstrating that mucosal allergic responses may disrupt gut motility, and may also potentially alter nociceptive pathways to cause visceral hyperalgesia.

RECENT FINDINGS

Experimental studies implicate T helper 2 cells and the cytokines interleukin-4 and -13 in antigen-induced dysmotility, and interleukin-5 in the pathogenesis of mucosal eosinophilia. Both mast cells and eosinophils play obligatory roles in different forms of experimental antigen-induced dysmotility. Overall clinical findings appear to implicate eosinophil infiltration in proximal and distal dysmotility syndromes (oesophageal, gastric and colorectal), and induced mast cell degranulation in mid-gut dysmotility. There is also evidence that mucosal allergic responses may induce long-term changes in visceral perception, including alteration of limbic response, leading to sustained abnormality in visceral sensation.

SUMMARY

Clinical evidence implicating mucosal allergic responses in dysmotility has been extended to include disorders considered previously entirely functional, such as in some cases of irritable bowel syndrome. Only a proportion of cases are, however, caused by food allergy and a future challenge is to differentiate patients with similar symptoms, but induced by different mechanisms.

Mast cell stabilizer ketotifen [4-(1-methyl-4-piperidylidene)-4h-benzo[4,5]cyclohepta[1,2-b]thiophen-10(9H)-one fumarate] prevents mucosal mast cell hyperplasia and intestinal dysmotility in experimental Trichinella spiralis inflammation in the rat

Trichinella spiralis infection in rats induces hypermotility and an abnormal response to cholecystokinin (CCK) similar to motor disturbances observed in irritable bowel syndrome. Mast cell hyperplasia is also characteristic of this experimental model. The aim of our study was to correlate mast cell activity with the development of dysmotility and to demonstrate whether the mast cell stabilizer ketotifen [4-(1-methyl-4-piperidylidene)-4H-benzo[4,5]cyclohepta[1,2-b]thiophen-10(9H)-one fumarate] could prevent the development of intestine hypermotility. Sprague-Dawley rats were infected with T. spiralis and, 5 days after infection, treated with the mast-cell stabilizer ketotifen (10 mg/kg/day). Twelve days after infection, intestinal spontaneous motor activity and response to CCK were evaluated by means of strain-gauge transducers. Immunohistochemistry for rat mast cell protease II (RMCPII), cyclooxygenase (COX)-2, and inducible nitric-oxide synthase (iNOS) was performed in intestinal specimens. In addition, RMCPII and myeloperoxidase were determined in serum. Infected control rats showed hypermotility, mast cell hyperplasia, increased RMCPII levels, increased myeloperoxidase, and overexpression of COX-2 and iNOS. In contrast, ketotifen-treated rats showed spontaneous intestinal motility and CCK response similar to the noninfected control rats. Mast cell hyperplasia and RMCPII were reduced in ketotifen-treated rats. Inflammatory parameters were less modified by ketotifen, but those animals that received the longest ketotifen treatment showed a slight amelioration in these parameters. These results indicate that mast cells are implicated in the development of hypermotility. The treatment with ketotifen prevented hypermotility and mast cell hyperplasia and diminished mucosal mast cell activity.

Contribution of 5-HT2A receptor in nematode infection-induced murine intestinal smooth muscle hypercontractility

BACKGROUND & AIMS

Enteric nematode infection induces a smooth muscle hypercontractility that depends on interleukin (IL)-4 and IL-13 activation of the signal transducer and activator of transcription (STAT) 6. Serotonin (5-HT) is involved in the physiologic regulation of gut function. The present study investigated the contribution of 5-HT and its receptors in nematode-induced intestinal smooth muscle hypercontractility.

METHODS

Mice were infected with Nippostrongylus brasiliensis (N brasiliensis) or Heligmosomoides polygyrus (H polygyrus) or injected intravenously with IL-13. Segments of jejunum were suspended in organ baths, and smooth muscle responses to 5-HT were determined in the presence or absence of specific 5-HT antagonists. IL-4, IL-13, and 5-HT receptor messenger RNA expressions were determined by real-time quantitative polymerase chain reaction.

RESULTS

5-HT evoked a modest contraction of smooth muscle in wild-type (WT) mice that was unaltered by the 5-HT2A antagonist ketanserin. N brasiliensis infection induced a smooth muscle hypercontractility to 5-HT that was abolished by 5-HT(2A) antagonists but not by other 5-HT antagonists. Infection-induced up-regulation of 5-HT2A expression was correlated with the smooth muscle hypercontractility to 5-HT. The infection-induced up-regulation of 5-HT2A in WT mice was observed also in IL-4(-/-) mice but was not seen in IL-13(-/-) or STAT6(-/-) mice. In addition, smooth muscle responses to 5-HT and 5-HT2A expression in WT mice were also enhanced by IL-13 or H polygyrus infection.

CONCLUSIONS

These data show that 5-HT2A is one of the molecules downstream from STAT6 activation that mediates changes in smooth muscle function. 5-HT2A represents a novel therapeutic target for modulating immune-mediated effects on intestinal motility.

5-Amino-2-hydroxybenzoic acid 4-(5-thioxo-5H-[1,2]dithiol-3yl)-phenyl ester (ATB-429), a hydrogen sulfide-releasing derivative of mesalamine, exerts antinociceptive effects in a model of postinflammatory hypersensitivity

H(2)S functions as a neuromodulator and exerts anti-inflammatory activities. Recent data indicate that irritable bowel syndrome (IBS) is linked to inflammation of the gastrointestinal tract. In this study, we have investigated the role of a novel H(2)S-releasing derivative of mesalamine (5-amino-2-hydroxybenzoic acid 4-(5-thioxo-5H-[1,2]dithiol-3yl)-phenyl ester, ATB-429) in modulating nociception to colorectal distension (CRD), a model that mimics some features of IBS, in healthy and postcolitic rats. Four graded (0.4-1.6 ml of water) CRDs were produced in conscious rats, and colorectal sensitivity and pain were assessed by measuring the abdominal withdrawal response and spinal c-Fos expression. In healthy rats, ATB-429 dose dependently (25, 50, or 100 mg/kg) attenuated CRD-induced hypersensitivity and significantly inhibited CRD-induced overexpression of spinal c-FOS mRNA, whereas mesalamine had no effect. ATB-429-induced antinociception was reversed by glibenclamide, a ATP-sensitive K(+) (K(ATP)) channel inhibitor. The antinociceptive effect of ATB-429 was maintained in a rodent model of postinflammatory hypersensitivity (4 weeks after colitis induction). At a dose of 100 mg/kg, ATB-429 reversed the allodynic response caused by CRD in postcolitic rats. Colonic cyclooxygenase-2 and interkeukin-1beta mRNA and spinal c-FOS mRNA expression were significantly down-regulated by ATB-429, but not by mesalamine. ATB-429, but not mesalamine, increased blood concentrations of H(2)S in both healthy and postcolitic rats. Taken together, these data suggest that ATB-429 inhibits hypersensitivity induced by CRD in both healthy and postcolitic, allodynic rats by a K(ATP) channel-mediated mechanism. This study provides evidence that H(2)S-releasing drugs might have beneficial effects in the treatment of painful intestinal disorders.

Gut motor function: immunological control in enteric infection and inflammation

Alteration in gastrointestinal (GI) motility occurs in a variety of clinical settings which include acute enteritis, inflammatory bowel disease, intestinal pseudo-obstruction and irritable bowel syndrome (IBS). Most disorders affecting the GI tract arise as a result of noxious stimulation from the lumen via either microbes or chemicals. However, it is not clear how injurious processes initiated in the mucosa alter function in the deeper motor apparatus of the gut wall. Activation of immune cells may lead to changes in motor-sensory function in the gut resulting in the development of an efficient defence force which assists in the eviction of the noxious agent from the intestinal lumen. This review addresses the interface between immune and motor system in the context of host resistance based on the studies in murine model of enteric nematode parasite infection. These studies clearly demonstrate that the infection-induced T helper 2 type immune response is critical in producing the alterations of infection-induced intestinal muscle function in this infection and that this immune-mediated alteration in muscle function is associated with host defence mechanisms. In addition, by manipulating the host immune response, it is possible to modulate the accompanying muscle function, and this may have clinical relevance. These observations not only provide valuable information on the immunological control of gut motor function and its role in host defence in enteric infection, but also provide a basis for understanding pathophysiology of gastrointestinal motility disorders such as in IBS.

Long-lasting changes in small intestinal transport following the recovery from Trichinella spiralis infection

Changes in intestinal motility and visceral sensitivity are found after resolution of acute enteric inflammation. The study investigates whether a transient nematode-induced intestinal inflammation may result in long-lasting remodelling of epithelial transport. Ferrets infected with Trichinella spiralis or sham-infected animals were euthanized on day 10, 30 or 60 postinfection (PI) and the jejunum was isolated. The net transport of electrolytes was measured electrophysiologically as transmucosal short-circuit current (I(sc)) and responses to electrical field stimulation (EFS: 1-32 Hz) or secretagogues were investigated. Myeloperoxidase (MPO) activity, a marker of mucosal inflammation, was maximal during the enteric stage of T. spiralis infection (day 10 PI) and returned to normal on days 30 and 60 PI. Mucosal inflammation caused a reduction in basal I(sc), increased electrical conductance (G) and decreased the maximal responses to EFS, carbachol or histamine. On days 30 and 60 PI the inflammation resolved and basal electrogenic transport appeared normal; however, the secretion induced by EFS, carbachol or histamine remained suppressed. Moreover, EFS-induced responses were shifted from predominantly cholinergic in controls to non-cholinergic in the infected animals. The results suggest that a transient small intestinal inflammation causes a long-term remodelling of epithelial function.

Intestinal epithelial cell signalling and host-derived negative regulators under chronic inflammation: to be or not to be activated determines the balance towards commensal bacteria

Advancing knowledge regarding the cellular mechanisms of intestinal inflammation has led to a better understanding of the disease pathology in patients with chronic disorders of the gut including inflammatory bowel disease, coeliac disease, lymphocytic colitis and irritable bowel syndrome. An emerging new paradigm suggests that changes in the homeostasis of bacteria- and host-derived signal transduction at the epithelial cell level may lead to functional and immune disturbances of the intestinal epithelium. It has become clear from numerous studies that enteric bacteria are a critical component in the development and prevention/treatment of chronic intestinal inflammation. Signal-specific activation of mitogen-activated protein kinases (MAPK), interferon-regulated factors (IRF) and the transcription factor NF-kappaB through pattern recognition receptor signalling effectively induce inflammatory defence mechanisms. Unbalanced activation of these innate signalling pathways because of host genetic predispositions and/or the lack of adequate anti-inflammatory feedback mechanisms may turn a physiological response into a pathological situation including failure of bacterial clearance and development of chronic inflammation. Host-derived regulators from the immune and enteric nerve system crosstalk to the innate signalling network of the intestinal epithelium in order to shape the extent and duration of inflammatory processes.

Post-infectious irritable bowel syndrome

PURPOSE OF REVIEW

Irritable bowel syndrome patients form a heterogeneous group with a variable contribution of central and peripheral components. The peripheral component is prominent in irritable bowel syndrome developing after infection (post-infectious irritable bowel syndrome) and this has proved a profitable area of research.

RECENT FINDINGS

Recent studies have overthrown the dogma that irritable bowel syndrome is characterized by no abnormality of structure by demonstrating low-grade lymphocytic infiltration in the gut mucosa, increased permeability and increases in other inflammatory components including enterochromaffin and mast cells. Furthermore, increased inflammatory cytokines in both mucosa and blood have been demonstrated in irritable bowel syndrome. While steroid treatment has proved ineffective, preliminary studies with probiotics exerting an anti-inflammatory effect have shown benefit.

SUMMARY

The study of post-infectious irritable bowel syndrome has revealed the importance of low-grade inflammation in causing irritable bowel syndrome symptoms. It has suggested novel approaches to irritable bowel syndrome including studies of serotonin and histamine metabolism which may be relevant to other subtypes of the disease.

Role of inhibitory neurotransmitter of myoenteric plexus in carcinogenesis of irritable bowel syndrome with different subtypes

AIM: To investigate the role of inhibitory neurotransmitter of myoenteric plexus in the carcinogenesis of constipation and diarrhea-predominant irritable bowel syndrome (C-IBS and D-IBS) in rats.

METHODS: Rat model of D-IBS was established by intracolonic instillation of acetic acid and restraint stress, while the positive and blank control were designed; Rat model of C-IBS was established by stomach irrigation with 0-4°C cool water daily for 14 d, while the positive and blank control were also designed. The bowel movement, the properties of fecal pellets, visceral sensitivity, and the content of nitric oxide (NO) in the myoenteric plexus were detected in the rats of each group.

RESULTS: The contraction frequency of the abdominal muscle in D-IBS group was significantly enhanced as compared with that in C-IBS, positive and blank control group (1.2 mL volume: 7.22±2.01 vs 2.77±0.78, 2.89±1.17, 3.59±1.08; 1.6 mL volume: 8.11±1.94 vs 2.89±1.67, 2.44±1.42, 2.89±1.22, P < 0.05) at high intensities of colorectal distention (CRD); while at low intensities of CRD, the contraction frequency in C-IBS group was significantly reduced as compared with that in D-IBS group (0.4 mL volume: 0.44±0.22 vs 2.44±0.67; 0.8 mL volume: 1.56±0.74 vs 6.31±1.74, P < 0.05). The amount, wet weight, and water ratio of the feces expelled by the rats in C-IBS and positive control group were significantly lower than those in blank control group (2.00±0.66, 2.33±0.50 vs 3.67±1.00; 0.80±0.32, 1.69±0.49 vs 2.14±0.27; 39.24±3.11, 40.67±2.84 vs48.38±2.79, P < 0.05); while the weight and water ratio of the feces in D-IBS group were markedly higher than those in positive and blank control group (2.31±0.72 vs 1.52±0.58, 1.57±0.56, P < 0.05; 65.31±3.31 vs 53.41±2.73, 55.78±3.99, P < 0.05). The time before the first melena defecation in C-IBS group was significantly longer than that in positive and blank controls (277.89±25.08 vs 205.44±15.74, 189.22±18.45, P < 0.05). There were no signs of colonic inflammation in the rats of each group. The number of NO positive neurons in rats of the C-IBS group was notably larger than that in D-IBS and blank control group (303.50±14.43 vs 200.89±16.67, 185.78±16.66, P < 0.01), but no obvious difference existed between D-IBS and blank control group (P >0.05).

CONCLUSION: The enhanced inhibitory neurotransmitter NO in the myoenteric plexus of colon is related to the IBS subgroups, visceral sensitivity, and motility dysfunction. The result reveals that the change of NO is related to the occurrence of different IBS subgroups.